EP0500416B1 - Method for producing oxygen by adsorption - Google Patents

Description

• a) une étape de production d'oxygène de durée x par soutirage de gaz selon une direction dite à co-courant, d'une colonne d'adsorbant du type zéolithe, à pression haute comprenant une pression maximale de cycle PM, avec admission d'air au moins partiellement au cours de cette étape ;
• b) une étape de pompage de durée y à contre-courant, sous pression sous-atmosphérique, opérant une dépressurisation, pompage qui se poursuit, le cas échéant, pendant une purge par passage à contre-courant de gaz enrichi en oxygène, la pression minimale de cycle atteinte au cours de ladite étape de pompage étant Pm ;
• c) une étape de repressurisation incorporant au plus tard avant l'étape de pompage, au moins une phase de repressurisation à contre-courant avec du gaz enrichi en oxygène.
  Voit à cet égard le document EP-A-0 248 720 qui enseigne un tel procédé comportant au moins quatre adsorbeurs.
  Cette façon de faire, destinée à la production industrielle de l'oxygène par fractionnement de l'air sur zéolithes, par exemple de type 5A ou 13X, fournit de l'air enrichi en oxygène, jusqu'à des teneurs en oxygène de 95%, les 5% résiduels étant essentiellement constitués d'argon.
  Dans un grand nombre d'applications, une qualité de production à 90/93% de teneur en oxygène est suffisante. Dans cette même gamme de teneurs, les quantités d'oxygène exigées par l'application peuvent aller de quelques tonnes/jour à quelques centaines de tonnes/jour.
  Le procédé rappelé plus haut s'est développé dans la gamme 10 à 50 T/jour d'oxygène, où il s'est révélé très compétitif en coût de revient par rapport à l'oxygène obtenu par voie cryogénique et livré sous forme liquide, ou par canalisation.
  Les différents types de cycles proposés pour la production d'oxygène comprennent généralement de deux à quatre adsorbeurs avec un seul adsorbeur en production, tandis que l'autre (ou les autres) sont soit en régénération, soit en phase intermédiaire (recyclage, repressurisation.....).
  Les cycles ayant une durée généralement comprise entre 90 secondes et quelques minutes, le volume des adsorbeurs pour un cycle donné, d'une durée déterminée, et avec un même type d'adsorbant, croît proportionnellement au débit à produire. Le respect des règles de vitesse de passage du gaz dans certaines phases impose une section minimale à la traversée du gaz, ce qui, pour des grandes tailles, devient directement ou indirectement le facteur limitant. Pour les adsorbeurs à géométrie cylindrique verticale et circulation verticale de gaz, c'est le diamètre des adsorbeurs qui devient excessif au-delà d'une certaine taille d'appareil (limitation du diamètre des fonds et viroles, problèmes de transport, etc...).
  Pour les adsorbeurs à géométrie cylindrique horizontale et circulation verticale de gaz, qui permettent de passer des débits plus grands que dans le cas précédent, à égalité de diamètre, le passage aux grands débits soulève les problèmes de distribution du gaz dans les collecteurs internes de part et d'autre de l'adsorbant, ainsi que l'augmentation importante des volumes morts dans ces collecteurs. On peut ainsi estimer à environ 60 T/jour la limitation d'une telle unité.
  Dans le cas où l'application exige des quantités en air suroxygéné ou en oxygène plus importantes, par exemple 300 T/jour, la solution actuelle est, soit d'installer plusieurs unités en parallèle (par exemple 3 unités de 50 T/jour chacune pour une demande de 150 T/jour), soit de passer à la solution par voie cryogénique.
  Le but de la présente invention est de repousser les limites actuelles en tonnage d'oxygène produit par unité de production. Plus précisément, l'objectif est de produire, sur une seule unité, une quantité d'oxygène qui pourrait être très supérieure à 60 T/jour, ce qui dans le coût de production diminuera la part de frais fixes (génie civil, engineering, montage, démarrage). Un autre objectif de l'invention est d'accroître la productivité de façon à réduire encore le coût de production par rapport à la mise en oeuvre de plusieurs unités de production, l'augmentation de productivité se traduisant par une diminution de l'investissement (matériel, adsorbant....). Encore un autre objectif de l'invention est de réduire la consommation d'énergie ce qui réduira encore le coût de production de l'oxygène.
  Ces objectifs de l'invention sont atteints par la prise en compte des mesures opératoires suivantes prises en combinaison globale :
• d) le nombre d'adsorbeurs est d'au moins trois ;
• e) la vitesse maximale du gaz traversant une colonne d'adsorption est inférieure à la vitesse d'attrition de l'adsorbant à un moment quelconque du cycle, et tend vers ladite limite au cours d'au moins une des étapes du cycle;
• f) la durée de pompage y sous pression sous-atmosphérique pendant l'étape b) est supérieure au déphasage T/n, et au moins égale à la durée x de l'étape de production ;
• g) la phase de pompage de la colonne d'adsorbant s'effectue en mettant en oeuvre sur ladite colonne d'adsorption successivement au moins deux systèmes de pompage opérant l'un à partir du début de pompage, un autre adapté à opérer jusqu'à la fin du pompage.

The present invention relates to the production of oxygen by adsorption of nitrogen from the air, of the kind where, on a plurality n of adsorbent columns, one successively, cyclically, is provided on one of said columns, with time shift T / n from one column to the next, T being the cycle period:

• a) a step of producing oxygen of duration x by drawing off gas in a direction known as co-current, from a column of adsorbent of the zeolite type, at high pressure comprising a maximum pressure of the PM cycle, with admission d air at least partially during this step;
• b) a pumping step of duration y against the current, under atmospheric pressure, operating a depressurization, pumping which continues, if necessary, during a purge by passage against the current of oxygen-enriched gas, the pressure minimum cycle reached during said pumping step being Pm;
• c) a repressurization step incorporating at least before the pumping step, at least one repressurization phase against the current with oxygen-enriched gas.
  See in this respect the document EP-A-0 248 720 which teaches such a process comprising at least four adsorbers.
  This procedure, intended for the industrial production of oxygen by fractionating air on zeolites, for example of the 5A or 13X type, provides air enriched with oxygen, up to oxygen contents of 95%. , the remaining 5% essentially being made up of argon.
  In a large number of applications, a production quality with 90/93% oxygen content is sufficient. In this same range of contents, the quantities of oxygen required by the application can range from a few tonnes / day to a few hundred tonnes / day.
  The process mentioned above has developed in the 10 to 50 T / day oxygen range, where it has proven to be very competitive in cost compared to oxygen. obtained cryogenically and delivered in liquid form, or by pipeline.
  The different types of cycles proposed for the production of oxygen generally include two to four adsorbers with a single adsorber in production, while the other (or the others) are either in regeneration, or in the intermediate phase (recycling, repressurization. ....).
  As the cycles generally have a duration of between 90 seconds and a few minutes, the volume of the adsorbers for a given cycle, of a determined duration, and with the same type of adsorbent, increases in proportion to the flow rate to be produced. Compliance with the gas passage speed rules in certain phases imposes a minimum section on the gas passage, which, for large sizes, becomes directly or indirectly the limiting factor. For the adsorbers with vertical cylindrical geometry and vertical gas circulation, it is the diameter of the adsorbers which becomes excessive beyond a certain size of device (limitation of the diameter of the bottoms and ferrules, transport problems, etc.) .).
  For adsorbers with horizontal cylindrical geometry and vertical gas circulation, which allow higher flow rates than in the previous case, with equal diameter, switching to high flow rates raises the problems of gas distribution in the internal manifolds. and other of the adsorbent, as well as the significant increase in dead volumes in these collectors. We can thus estimate at around 60 T / day the limitation of such a unit.
  In the case where the application requires larger quantities of superoxygenated air or oxygen, for example 300 T / day, the current solution is either to install several units in parallel (for example 3 units of 50 T / day each for a request of 150 T / day), or to switch to the solution cryogenically.
  The aim of the present invention is to push the current limits in tonnage of oxygen produced per production unit. More specifically, the objective is to produce, on a single unit, an amount of oxygen that could be much more than 60 T / day, which in the production cost will reduce the share of fixed costs (civil engineering, engineering, mounting, starting). Another objective of the invention is to increase productivity so as to further reduce the production cost compared to the implementation of several production units, the increase in productivity resulting in a decrease in investment ( material, adsorbent ....). Yet another objective of the invention is to reduce energy consumption which will further reduce the cost of producing oxygen.
  These objectives of the invention are achieved by taking into account the following operating measures taken in overall combination:
• d) the number of adsorbers is at least three;
• e) the maximum speed of the gas passing through an adsorption column is lower than the attrition speed of the adsorbent at any time in the cycle, and tends towards said limit during at least one of the stages of the cycle;
• f) the duration of pumping y under sub-atmospheric pressure during step b) is greater than the phase shift T / n, and at least equal to the duration x of the production step;
• g) the pumping phase of the adsorbent column is carried out by implementing on said adsorption column successively at least two pumping systems, one operating from the start of pumping, another adapted to operate until at the end of pumping.

By attrition speed is meant a gas speed, in an adsorption column beyond which the adsorbent particles are set in motion. By pumping system means either a pump and its own motor, or a stage or pump body and in this case, several pumping systems can be connected to a single motor.

• on assure h) une dépressurisation entre l'étape de production et l'étape de pompage, de façon à fourni r du gaz de purge pour l'étape de purge éventuelle selon b) d'un autre adsorbeur ;
• on assure i) une dépressurisation à co-courant, entre l'étape de production et l'étape de pompage, de façon à fournir du gaz de repressurisation partielle pour l'étape c) de repressurisation ;
• on assure d'abord la dépressurisation selon i) puis la dépressurisation selon h) ;
• le gaz enrichi en oxygène de l'étape b) et/ou de l'étape c) est de l'oxygène de production ;
• le gaz de dépressurisation à co-courant est au moins partiellement introduit dans un stockage d'attente, duquel est prélevé au moins une partie du gaz de purge ;
• la phase de repressurisation à contre-courant selon c) s'effectue avec du gaz de production ;
• le gaz de production est stocké dans un réservoir tampon duquel est prélevé au moins une partie du gaz de repressurisation à contre-courant selon c) ;
• l'étape de production s'effectue au moins en partie à pression maximale ;
• l'étape de production s'effectue au moins en partie à pression croissante ;
• l'étape de production s'effectue au moins en partie à pression décroissante ;
• l'étape de repressurisation c) incorpore au moins une phase de repressurisation à co-courant avec de l'air ;
• la pression maximale de cycle PM est comprise entre 1.10⁵ et 1,6.10⁵ Pascal, tandis que la pression minimale de cycle est comprise entre 0,2.10⁵ et 0,5.10⁵ Pascal ;
• la durée de pompage selon b) est égale à un multiple entier de T/n ;
• le nombre d'adsorbeurs "n" est de quatre ;
• l'étape de pompage s'effectue avec deux systèmes de pompage sur une durée double de celle de l'étape de production qui est de T/n ;
• le nombre d'adsorbeurs est de cinq, l'étape de pompage est de durée égale à celle de l'étape de production qui est de 2T/5, le nombre d'adsorbeurs en production simultanée étant de deux à tout instant du cycle ;
• le nombre d'adsorbeurs est de six ou sept, le nombre de systèmes de pompage est de trois opérant pendant une durée de 3T/n, tandis que deux adsorbeurs sont en production simultanée pendant une durée de 2T/n et cela pendant tout le cycle.

The invention is more particularly implemented according to the following directives:

• h) is depressurized between the production step and the pumping step, so as to supply r purge gas for the optional purge step according to b) of another adsorber;
• there is provided i) a co-current depressurization, between the production step and the pumping step, so as to provide partial repressurization gas for step c) of repressurization;
• first, depressurization is provided according to i) then depressurization according to h);
• the oxygen-enriched gas from step b) and / or from step c) is production oxygen;
• the co-current depressurization gas is at least partially introduced into a holding storage, from which at least part of the purge gas is taken;
• the counter-current repressurization phase according to c) is carried out with production gas;
• the production gas is stored in a buffer tank from which at least part of the counter-current repressurization gas according to c) is taken;
• the production stage is carried out at least in part at maximum pressure;
• the production stage is carried out at least in part at increasing pressure;
• the production stage is carried out at least in part at decreasing pressure;
• the repressurization step c) incorporates at least one co-current repressurization phase with air;
• the maximum cycle pressure PM is between 1.10⁵ and 1.6.10⁵ Pascal, while the pressure minimum cycle is between 0.2.10⁵ and 0.5.10⁵ Pascal;
• the pumping time according to b) is equal to an integer multiple of T / n;
• the number of adsorbers "n" is four;
• the pumping stage is carried out with two pumping systems over a duration double that of the production stage which is T / n;
• the number of adsorbers is five, the pumping step is of duration equal to that of the production step which is 2T / 5, the number of adsorbers in simultaneous production being two at any time of the cycle;
• the number of adsorbers is six or seven, the number of pumping systems is three operating for a duration of 3T / n, while two adsorbers are in simultaneous production for a duration of 2T / n and this throughout the cycle .

It is by comparing the cycle of the invention with a known cycle which is related to it (same steps with adsorbers filled with the same adsorbent, but of smaller number), that increases in "production" (tonnes / day) of at least 50% and up to 300% and increases in productivity (Nm³ / h / m³ adsorbent) of at least 10% and more generally from 12% to 20% according to the various optional measures mentioned above -above.

It is by increasing the number of adsorbers compared to the known cycle which is related to it, while keeping a cycle time substantially similar, that one can increase the production per unit.

It is by increasing the number of adsorbers compared to the known cycle which is related to it, that we can better optimize the phase or step times, while respecting their own limits, which leads to a more efficient, and in particular more productive.

It is by increasing the number of adsorbers compared to the known cycle which is related to it, by multiplying the number of adsorbers simultaneously in pumping, that several pumping systems can be used, each of them being adapted to the specific pressure range for which it is used.

The invention is now illustrated with reference to the accompanying drawings in which FIGS. 1 to 13 represent the pressure (ordered) -time diagrams (abscissa) of thirteen implementation variants, the pressure varying between a maximum pressure of the cycle PM (between 1.10⁵ and 1.6.10⁵ Pascal) and a minimum pressure Pm of the cycle (between 0.2.10⁵ and 0.5.10⁵ Pascal).

In all the variants of FIGS. 1 to 10 and 12 to 13, the pressure-time diagram (t) is established at time 0 by the start of the oxygen production phase (passage of air in the adsorption column according to the direction of circulation known as co-current conventionally represented by an arrow in the direction of the ordinate oriented in the direction of increasing ordinates), while a circulation, against the current, which is opposite to that of the production stage, that is to say from the "outlet" of the oxygen produced towards the "inlet" of the air to be fractionated, is represented by an arrow in the direction of the ordinate oriented towards the ordinates decreasing.

These different arrows are connected either at the free end, towards the increasing ordinates to indicate a rate of production of oxygen, or of air enriched in oxygen, or oriented towards the decreasing ordinates to indicate a pumping under sub-atmospheric pressure.

The durations of the different stages are noted in circles and the duration of the cycle T is the highest time indicated on the abscissa.

This being explained, we now detail the different cycles illustrating the invention, which include certain phases or stages among which, a production stage, a phase of first depressurization, a second depressurization phase, a pumping step possibly comprising a purge phase and a repressurization step. The pumping step is carried out by implementing a plurality of pump 1, pump 2, etc. pumping systems.

The times indicated in the following descriptions are given by way of example, and are appreciably suitable for the use of adsorbent of medium particle size (balls with an average diameter of approximately 2 mm or cylindrical rods with a diameter of 1.6 mm).

Figure 1

Cycle time T 120 sec. Number of adsorbers n 4 Adsorbers in production 1 Production stage duration 30 sec. Duration of first depressurization 10 sec. Pumping time 60 sec. Purge time 10 sec. Pumping systems of them Repressurization time 20 sec.

FIGURE 2

Cycle time T 112.5 sec. Number of adsorbers n 5 Adsorbers in production 2 Production stage duration 42.5 sec. Duration of first depressurization 10 sec. Pumping time 45 sec. Purge time 10 sec. Pumping systems of them Repressurization time 15 sec.
It is noted that there is a buffer tank R on the production gas to regulate the useful production flow rate and best complete the final repressurization.

FIGURE 3

Cycle time T 120 sec. Number of adsorbers n 6 Adsorbers in production 1.5 Production stage duration 30 sec. Duration of first depressurization 10 sec. Pumping time 60 sec. Purge time 10 sec. Pumping systems three Repressurization time 20 sec.

FIGURE 4

Cycle time T 105 sec. Number of adsorbers n 7 Adsorbers in production 2 Production stage duration 30 sec. Duration of first depressurization 15 sec. Pumping time 45 sec. Purge time 15 sec. Pumping systems three Repressurization time 15 sec.

FIGURE 5

Cycle time T 120 sec. Number of adsorbers n 4 Adsorbers in production 1 Production stage duration 30 sec. Duration of first depressurization 10 sec. Pumping time 60 sec. Purge time 10 sec. Pumping systems of them Repressurization time 20 sec.

It is noted that there is a holding tank S for a shorter repressurization than the production stage, so as to equalize the useful production flow.

FIGURE 6

Cycle time T 120 sec. Number of adsorbers n 4 Adsorbers in production 1 Production stage duration 30 sec. Duration of first depressurization 10 sec. Pumping time 50 sec. Purge time 10 sec. Pumping systems of them Repressurization time 30 sec.

Note the existence of a storage tank S ′ which makes it possible to defer the use in purging of the gas of first depressurization, when this first depressurization does not coincide in time with said purging of another adsorber.

FIGURE 7

Cycle time T 120 sec. Number of adsorbers n 4 Adsorbers in production 1 Production stage duration 30 sec. Duration of first depressurization 10 sec. Pumping time 50 sec. Purge time 15 sec. Pumping systems of them Repressurization time 30 sec.

It is noted that the first depressurization is used at the start of repressurization of another adsorber while the purge gas is a flow rate taken, during half of the production step, on the oxygen produced. A variant of the first repressurization has been shown in dashes according to which, in addition to the gas coming from the adsorber in the first depressurization, production gas is added.

FIGURE 8

Cycle time T 120 sec. Number of adsorbers n 4 Adsorbers in production 1 Production stage duration 30 sec. Pumping time 60 sec. Pumping systems of them Repressurization time 30 sec.

FIGURE 9

Cycle time T 125 sec. Number of adsorbers n 5 Adsorbers in production 2 Production stage duration 50 sec. Pumping time 50 sec. Pumping systems of them Repressurization time 25 sec.

FIGURE 10

Cycle time T 120 sec. Number of adsorbers n 6 Adsorbers in production 2 Production stage duration 40 sec. Pumping time 60 sec. Pumping systems three Repressurization time 20 sec.

FIGURE 11

Cycle time T 135 sec. Number of adsorbers n 3 Adsorbers in production 1 part-time Production stage duration 20 sec. Duration of first depressurization 10 sec. Pumping time 80 sec. Pumping systems of them Repressurization time - air + enriched air 10 sec. - air alone 15 sec.

FIGURE 12

Cycle time T 120 sec. Number of adsorbers n 4 Adsorbers in production 1 Production stage duration 30 sec. Duration of first depressurization 10 sec. Duration of second depressurization 5 sec. Pumping time 45 sec. Purge time 10 sec. Pumping systems of them Repressurization time 30 sec.

FIGURE 13

Cycle time T 125 sec. Number of adsorbers n 5 Adsorbers in production 2 Production stage duration 50 sec. Duration of first depressurization 10 sec. Pumping time 50 sec. Purge time 10 sec. Pumping systems of them Repressurization time 15

Claims (18)

1. Process for the production of a gas having up to 95 % oxygen content notably at a flow rate greater than 60 T/day by means of absorbing the nitrogen in the air such that, on a plurality "n" of adsorbent columns, the following stages are ensured successively and cyclically for a period T on each of the said columns with a time lag of T/n, from one column to the next :

   a) a stage for the production of oxygen of duration x by withdrawing gas in a so-called co-current direction, from an adsorbent column of the zeolite type, at high pressure comprising a maximum cycle pressure PM, with at least partial admission of air during this stage ;

   b) a counter-current pumping stage of duration y, under sub-atmospheric pressure, bringing about depressurization, pumping being carried out, as appropriate, during a purge by passing gas enriched in oxygen in a counter-current direction, the minimum cycle pressure attained during the said pumping stage being Pm ;

   c) a repressurization stage incorporating before the pumping stage at the latest, at least one counter-current repressurization phase with gas enriched in oxygen ; characterized by a combination of the following measures :

   d) the number of adsorbers is at least three ;

   e) the maximum velocity of the gas passing through an adsorption column is less than the attrition rate of the adsorbent at any moment whatsoever in the cycle, and tends towards the said limit during at least one of the stages of the cycle :

   f) the duration of pumping y under sub-atmospheric pressure during stage b) is greater than the time lag T/n, and at least equal to the duration x of the production stage ;

   g) the pumping stage of the adsorbent column is carried out by successively putting into operation at least two pumping systems on the said column, one operating from the start of pumping and the other adapted to operate until the end of pumping.
2. Process for the production of oxygen according to Claim 1, characterized in that counter-current depressurization h) is ensured between the production stage and the pumping stage, so as to provide a purge gas for the possible purging according to b) of another adsorber.
3. Process for the production of oxygen according to Claim 1, characterized in that a counter-current depressurization i) is ensured between the production stage and the pumping stage, so as to provide partially repressurized gas for the repressurization stage c).
4. Process for the production of oxygen according to Claims 2 and 3, characterized in that depressurization is first of all ensured according to i) followed by depressurization according to h).
5. Process for the production of oxygen according to any one of Claims 1 to 4, characterized in that the gas enriched in oxygen of stage b) and/or of stage c) is production oxygen.
6. Process for the production of oxygen according to Claim 2, characterized in that the counter-current depressurization gas is at least partially introduced into a holding store, from which at least part of the purge gas is taken.
7. Process for the production of oxygen according to any one of Claims 1 to 6, characterized in that the counter-current repressurization phase of the repressurization stage c) is carried out with production gas.
8. Process for the production of oxygen according to Claim 7, characterized in that a buffer stock of production gas is provided from which at least part of the counter-current repressurization gas according to c) is taken.
9. Process for the production of oxygen according to any one of Claims 1 to 8, characterized in that the production stage is carried out at least partly at maximum pressure.
10. Process for the production of oxygen according to any one of Claims 1 to 9, characterized in that the production stage is carried out at least partly at increasing pressure.
11. Process for the production of oxygen according to any one of Claims 1 to 10, characterized in that the production stage is carried out at least partly at decreasing pressure.
12. Process for the production of oxygen according to any one of Claims 1 to 11, characterized in that the repressurization stage c) incorporates at least one counter-current repressurization phase with air.
13. Process for the production of oxygen according to any one of Claims 1 to 12, characterized in that the maximum cycle pressure PM lies between 1×10⁵ and 1.6×10⁵ Pascal, whilst the minimum cycle pressure lies between 0.2 × 10⁵ and 0.5 × 10⁵ Pascal.
14. Process for the production of oxygen according to any one of Claims 1 to 13, characterized in that the duration of pumping according to b) is equal to a whole multiple of T/n.
15. Process for the production of oxygen according to any one of Claims 1 to 14, characterized in that the number "n" of adsorbers is four.
16. Process for the production of oxygen according to Claim 15, characterized in that the pumping stage is carried out with two pumping systems over a period double that of the production stage which is T/n.
17. Process for the production of oxygen according to any one of Claims 1 to 14, characterized in that the number of adsorbers is five and in that the pumping stage lasts for a period equal to that of the production stage which is 2T/5, the number of adsorbers in simultaneous production being two at any instant of the cycle.
18. Process for the production of oxygen according to any one of Claims 1 to 14, characterized in that the number of adsorbers is six or seven and in that the number of pumping systems is three operating for a period of 3T/n, whilst two adsorbers are at any instant in simultaneous production over a period of 2T/n.

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